[X86] Add -x86-experimental-vector-widening-legalization check to...

[X86] Add -x86-experimental-vector-widening-legalization check to combineSelect and combineSetCC to cover vXi16/vXi8 promotion without BWI.

I don't yet have any test cases for this, but its the right thing to do based on log file inspection.

llvm-svn: 347151